This invention relates generally to semiconductor manufacturing equipment, and more particularly to traps and filters for removing gaseous materials from exhaust gasses of semiconductor manufacturing equipment.
Semiconductor wafers are processed within processing chambers of semiconductor manufacturing equipment to produce integrated circuits (ICs). For example, semiconductor wafers can be processed within a plasma etch machine to remove material from the wafer surface, or can be processed with in a chemical vapor deposition (CVD) machine to deposit layers of material over the wafer surface.
A common processing step is the deposition of a silicon-nitride passivation layer over a semiconductor wafer. One process for forming silicon-nitride layers is to react ammonia (NH.sub.3) with dichlorosilane (SiH.sub.2 Cl.sub.2) within a wafer processing chamber. Unfortunately, one of the by-products of the reaction is ammonium chloride (NH.sub.4 Cl) which is a gaseous material at processing temperatures (e.g. greater than about 300.degree. C. and typically about 700.degree. C.) but which forms a solid condensate at temperatures below about 125.degree. C.
A problem occurs when pumping waste gasses from a silicon-nitride processing chamber during processing. The ammonium chloride, which is initially in a gaseous state, condenses as a solid in the exhaust pipes and within the exhaust pump used to extract the waste gasses from the chamber. Ammonium chloride condensed in the exhaust pipes and pump can back-flow into the processing chamber under certain circumstances, which can contaminate the chamber and any wafer within the chamber. This type of contamination can produce a "nitride haze" on the wafers being processed with undesirable and sometimes damaging results.
Condensed ammonium chloride within the pump mechanism is particularly problematical. The pumps used are typically molecular pumps designed to pump very low pressure gasses. When ammonium chloride deposits within the pump mechanism, it forms a salt-like substance which grinds the delicate internal surfaces of the pump. This can lead to premature wear, reduced efficiency, and ultimately the failure of the pump.